共查询到20条相似文献，搜索用时 796 毫秒
1.
Numerical investigation of cavitating flow behind the cone of a poppet valve in water hydraulic system 总被引：2，自引：0，他引：2
Computational Fluid Dynamics (CFD) simulations of cavitating flow through water hydraulic poppet valves were performed using
advanced RNGk-epsilon turbulence model. The flow was turbulent, incompressible and unsteady, for Reynolds numbers greater than 43000. The
working fluid was water, and the structure of the valve was simplified as a two dimensional axisymmetric geometrical model.
Flow field visualization was numerically achieved. The effects of inlet velocity, outlet pressure, opening size as well as
poppet angle on cavitation intensity in the poppet valve were numerically investigated. Experimental flow visualization was
conducted to capture cavitation images near the orifice in the poppet valve with 30° poppet angle using high speed video camera.
The binary cavitating flow field distribution obtained from digital processing of the original cavitation image showed a good
agreement with the numerical result.
Project supported by the National Natural Science Foundation of China (No. 59835160) and Scientific Research Foundation for
Returned Overseas Chinese Scholars, State Education Ministry of China (No. 50175097) 相似文献
2.
针对智能雷弹要求其预警系统对目标快速识别和低功耗工作的特点,根据相关理论和模式识别技术,提出了直接分析所接收的直升机噪声时域信号的方法,即利用自相关函数估计信号基频,以被测信号基频为特征量进行目标识别的方法.仿真研究表明,该方法具有一定的实用性. 相似文献
3.
Orienting to one of two levels of stimulus significance (a distress squeal or a simulated mimic squeal) in female hooded rats was measured by suppression of ongoing drinking. Subsequent generalization tests with the same stimulus presented in different contexts showed that generalization of habituation across contexts was a function of stimulus significance: Habituation to the distress squeal was restricted to the context in which it first had been presented, whereas habituation to the mimic squeal generalized across the different contexts. 相似文献
4.
Three experiments measured orienting of rats to stimuli varying in intrinsic significance. In the first, rats showed greater reactivity to a recording of a conspecific’s distress squeal than to a simulated mimic squeal when the stimuli were presented at 100 dB but not at 80 dB, and orienting to all stimuli habituated rapidly with repeated stimulus exposures. Experiment 2 showed that, following several stimulus exposures, recovery of orienting after rest periods of 1 and 7 days was a function of the stimulus: Orienting to the distress squeal presented at 100 dB recovered more rapidly than did orienting to the mimic squeal at 100 dB or to either the mimic or the distress squeal presented at 80 dB. Experiment 3 showed that habituation to the most significant stimulus, the distress squeal presented at 100 dB, was retarded at long (24-h) interstimulus intervals, presumably a consequence of less stimulus-to-stimulus transfer of habituation with this stimulus. The results are discussed in terms of biological constraints on habituation of orienting and on recovery of orienting following habituation. 相似文献
5.
The paper reports results of investigation on the harmonic detection technique of a complicated power supply system such as
an AC excited generation system, which has a variable fundamental frequency and low order harmonics with rich sub-harmonics
whose frequencies are lower than the fundamental one. The in-phase correlation filtering technique, based on the frequency
shifting principle, is proposed in this paper. Theoretical analysis and experimental results validate the effectiveness of
this technique for the harmonic detections of AC excited generation systems.
Project (No. 59877021) supported by the National Natural Science Foundation of China. 相似文献
6.
A Model S195 (8.8 kW) single cylinder was used in this study to determine the effect of four operational parameters, i. e.
intake valve close angle, exhaust valve open angle, fuel delivery angle and fuel injection pressure on noise. Single factor
and multi-factor quadratic regressive orthogonal methods were adopted in the experiments to find the relationship between
the four parameters and noise. By means of optimization technique, the optimum operational parameters for two working conditions
of the engine were selected and the test results showed that optimum adjustment could reduce noise by 2–4 dB.
Project supported by Agricultural Ministry of China 相似文献
7.
ＮＴＲＯＤＵＣＴＩＯＮＴｙｐｅＳ1 95ｄｉｅｓｅｌｅｎｇｉｎｅｓａｒｅｗｉｄｅｌｙｕｓｅｄｉｎｒｕｒａｌａｒｅａｓｏｆＣｈｉｎａ.Ｔｈｅｔｏｔａｌｎｕｍｂｅｒｏｆｔｈｅｅｎ ｇｉｎｅｓｕｓｅｄｉｎａｇｒｉｃｕｌｔｕｒｅｉｓａｂｏｕｔ8ｍｉｌｌｉｏｎｓｅｔｓ.Ｏｕｒｉｎｖｅｓｔｉｇａｔｉｏｎｓｓｈｏｗｅｄｔｈａｔｔｈｅｗｏｒｋｉｎｇｃｏｎ ｄｉｔｉｏｎｓｏｆｔｈｅｅｎｇｉｎｅｓｉｎｕｓｅａｒｅｒｅｌａｔｉｖｅｌｙｂａｄｉｎｇｅｎｅｒａｌ.Ｔｈｅｎｏｉｓｅｌｅｖｅｌｉｓｖｅｒｙｈｉｇｈ .Ｔｒａｃｔｏｒｏｐｅ… 相似文献
8.
Werner Nitschke 《Learning & behavior》1979,7(4):457-460
Classically conditioned shock-elicited vocalizations in the adult rat were acoustically analyzed and described, The fundamental frequency of the CRs ranged between 2,000 and 3,600 Hz, with overtones that extended well into the ultrasonic range and with durations lasting approximately 1÷2 sec. Major differences between CR and UCR signals were apparent. The CR vocalizations had little frequency variation and little or no noise, while the UCR vocalizations were associated with highly irregular frequencies and broad-band noise. Post-shock vocalizations had combined features of the CR and UCR sounds. It is suggested that the differences between the CR and UCR are related to the CR being the emotional cry and the UCR the pain cry. 相似文献
9.
气垫阀的性能,很大程度上取决于阀隙马赫数、气阀升程、气阀弹簧力和气阀呼吸孔直径等主要性能参数的设计选取。本文介绍了设计气垫阀时选择这些主要参数的基本原理和方法。根据我国目前的实际和资料,介绍了气垫阀设计时确定这些主要参数的曲线图和计算公式,为气垫阀的设计计算提供了依据。 相似文献
10.
用试验方法研究了阀门的开启程度、支撑位置变化和管道内液体脉动对管道系统振动特性的影响．结果表明：由阀门开启程度引起的振动频率随着阀门开启程度的减小而增大;由可移动支撑位置改变引起的两个振动频率随着可移动支撑向中间的靠近而逐渐远离;由管道内液体脉动引起的振动频率随着可移动支撑向中间靠近和阀门开启程度的减小而减小． 相似文献
11.
首先对雷电流的波形进行分析,然后对雷电流的脉冲函数模型进行傅里叶变换,得出雷电流的频谱函数、雷电流峰值比率的频谱及雷电流峰值比率积累的频谱,在给定波形的条件下绘出雷电流的频谱图、雷电流峰值比率的频谱图及雷电流峰值比率积累的频谱图,然后找出雷电危害的重要波段所在。这对雷电防护装置的设计具有重要的指导意义。 相似文献
12.
Jian Han Shuo-qiao Zhong Xin Zhou Xin-biao Xiao Guo-tang Zhao Xue-song Jin 《浙江大学学报(A卷英文版)》2017,18(8):593-602
This paper develops a numerical model for wheel-rail noise analysis in the time-domain. This model for wheel-rail noise is based on vehicle-track coupling dynamics considering the effect of flexible wheelsets and track, and a transient wheel-rail noise prediction method. This model can approximatively characterize the components of vibration and noise in the frequency range up to 3.5 kHz. The wheel-rail forces are calculated and shown in both time and frequency domains by using the vehicletrack coupling dynamic model. Then the vibration and sound of the flexible wheelset are calculated by the transient finite elementboundary element (FE-BE) prediction model at 300 km/h, in which the effects of random irregularity and discrete supporting excitation are considered. The numerical results calculated by using the present model are discussed. The present model is also used to calculate the effect of corrugation with wavelengths of 40 mm to 300 mm on wheel-rail noise. The numerical results can be useful for academic research and engineering application to railway noise and vibration. 相似文献
13.
调节阀应用中技术问题的探讨 总被引：1，自引：0，他引：1
万卉丹 《河北能源职业技术学院学报》2005,5(4):62-64
选择和安装好调节阀,使调节阀在一个高水平状态下运行将是一个很关键的问题。收集完整的工艺流体的物理特性参数与调节阀的工作条件,掌握和确定调节阀体本身的结构、形式、材料等方面的特点,流量特性、压降、闪蒸、气蚀、噪音等问题,是选择调节阀考虑的重点。 相似文献
14.
用不同方法进行发动机噪声源识别的研究 总被引：9，自引：0，他引：9
发动机噪声源识别对于制定发动机降噪措施十分重要 ,而像油底壳、气门罩、前齿轮室盖等罩壳类零件通常是发动机的主要噪声源 .本文用铅覆盖法和表面振动测量法对一台六缸工程机械用柴油机进行了表面噪声源识别的研究 ,得到了罩壳类零件按噪声能量大小的排列顺序 ,文中首先在半消声条件下利用铅覆盖技术测量了这些罩壳类零件的声功率 ,然后又研究了它们的振动特性 ,并通过表面振动速度的面积时间均方值预测了其声功率 .两种方法的测量结果吻合较好 ,说明了它们在工程领域应用的有效性 相似文献
15.
电动截止阀是流体输送的重要元件.阀的传统设计方法很少从流体角度对其流道进行设计,其流阻系数比较大,容易造成局部压力损失.流体介质通过阀口时,流动方向发生变化,可能产生诸如局部涡流、空化、水锤和死水区等水流现象及湍流脉动噪声,对阀体有很强的破坏性,降低阀的使用寿命.基于RAN-S方程组和RNG k-ε湍流模型,利用CFD技术对全开启状态下的电动截止阀的内流道进行三维的湍流数值模拟,获得其总压图、速度矢量图、湍动能强度图.通过数值模拟,可以直观地显示阀的内流道中流体的流动过程.改变进出口段流道的长度、曲率以及阀杆在流道中的布局等,进出口的压力差相对于未改进前减少30%左右,速度突变区域明显缩小,局部涡流现象消失,湍动能强度也降低了15%左右. 相似文献
16.
Across several independent studies, infants from a few days to 9 months of age have shown preferences for infant-directed (ID) over adult-directed (AD) speech. Moreover, 4-month-olds have been shown to prefer sine-wave analogs of the fundamental frequency of ID speech, suggesting that exaggerated pitch contours are prepotent stimuli for infants. The possibility of similar preferences by 1-month-olds was examined in a series of experiments, using a fixation-based preference procedure. Results from the first 2 experiments showed that 1-month-olds did not prefer the lower-frequency pitch characteristics of ID speech, even though 1-month-olds were able to discriminate low-pass filtered ID and AD speech. Since low-pass filtering may have distorted the fundamental frequency characteristics of ID speech, 1-month-olds were also tested with sine-wave analogs of the fundamental frequencies of the ID utterances. Infants in this third experiment also showed no preference for ID pitch contours. In the fourth experiment, 1-month-olds preferred a natural recording of ID speech over a version which preserved only its lower frequency prosodic features. From these results, it is argued that, although young infants are similar to older infants in their attraction to ID speech, their preferences depend on a wider range of acoustic features (e.g., spectral structure). It is suggested that exaggerated pitch contours which characterize ID speech may become salient communicative signals for infants through language-rich, interactive experiences with caretakers and increased perceptual acuity over the first months after birth. 相似文献
17.
某系列空调器室外机测试时发现低频噪声,通过连接管或墙壁传到室内侧。分析和实验证明,这是由压缩机噪声和室外风扇噪声叠加而成的。通过系统优化设计,室外侧100Hz的噪声峰值降低了8dB（A）。 相似文献
18.
The most dominant error source for microwave ranging is the frequency instability of the oscillator that generates the carrier phase signal. The oscillator noise is very difficult to filter due to its extremely low frequency. A dual transponder carrier ranging method can effectively minimize the oscillator noise by combing the reference phase and the to-and-fro measurement phase from the same single oscillator. This method does not require an accurate time tagging system, since it extracts phases on the same satellite. This paper analyzes the dual transponder carrier ranging system by simulation of the phase measurements with comprehensive error models. Both frequency domain and time domain noise transfer characteristics were simulated to compare them with dual one-way ranging. The simulation results in the two domains conformed to each other and demonstrated that a high level of accuracy can also be achieved by use of the dual transponder carder ranging system, with relatively simple instruments. 相似文献
19.
Shear probe works under a tough environment where the turbulence signals to be measured are very weak.The measured turbulence signals often contain a large amount of noise.Due to wide frequency band,no... 相似文献
20.
徐爱华 《南通职业大学学报》2014,(4):85-88
针对水泥路面裂缝识别的干扰和噪声问题,提出一种基于图像增强的裂缝检测方法。首先利用小波变换增强裂缝对比度;再采用空域滤波和基于傅里叶变换（FFT）的频域滤波相结合的方法滤除图像中的噪声和干扰;在此基础上,使用边缘检测方法实现裂缝提取。实验结果表明,该方法可有效去除图像中的干扰和噪声,较好地识别水泥路面的裂缝。 相似文献